1. Field of Invention
The invention relates generally to micro-electro-mechanical systems (MEMS) and or micro-opto-electro-mechanical systems (MOEMS), and more specifically to apparatuses and methods used to harvest energy with a MEMS or MOEMS device.
2. Art Background
Modern society demonstrates an insatiable appetite for energy. This appetite for energy spans a wide spectrum of devices and uses such as implantable devices, e.g., pace makers, hearing aids, etc.; handheld devices, e.g., telephones, smart phones, tablets, laptop computers, global positioning system (GPS); and large devices that heat and cool buildings and power automobiles, trucks, busses, building, etc. The list is endless and the need continues to grow with no end in sight. While the need for energy exists across this wide spectrum of devices, often energy is wasted. Wasted energy, if collected, can be used as the primary source of energy for a device. Thus, a simultaneous need to collect wasted energy exists. Collection of wasted energy is also referred to as energy harvesting.
A class of materials called ferroelectrics, which includes piezoelectric materials, can be used to harvest energy. Ferroelectric materials can be combined with micro-electro-mechanical systems (MEMS) or micro-optical-electro-mechanical systems (MOEMS) to harvest energy, thereby turning wasted vibrational energy into electrical energy. As used herein such a device will be referred to as a T-MEMS energy harvester, where “T” refers to the “transduction” nature of the device, whereby electrical energy is generated by an induced strain in a transduction material that produces electrical energy in response to the strain. The resulting T-MEMS or T-MOEMS energy harvester can be coupled to a rechargeable battery to provide a source of electrical power which can power a multitude of devices. The efficiency of existing T-MEMS based harvesters has been low. This presents a problem.
Bending beam based resonance devices have been made which include a piezoelectric material such as lead zirconate titanate ceramic (PZT) or polyvinylidene fluoride (PVDF) combined with a mechanical structure that is designed to subject the piezoelectric material to strain through vibration. However, due to the finite non-zero stiffness of the support structure and the ferroelectric material, a significant amount of energy goes into overcoming the bending stiffness of the combined support structure/ferroelectric material to the detriment of the systems ability to harvest energy. This presents a problem.